1. Field of the Invention
The present invention relates to a movable contactor for an air circuit breaker, and particularly, to a movable contactor for an air circuit breaker with a contact spring protecting mechanism which is capable of minimizing damage to contact springs due to arcs occurred upon a tripping operation.
2. Background of the Invention
An air circuit breaker refers to an electric apparatus which can manually or automatically block a relatively low voltage circuit among power receiving and distributing apparatuses, thus to diverge the low voltage circuit and protect circuits and equipment. The air circuit breaker includes contactor portions provided with a stationary contactor connected to a circuit of a power source or a electric load, and a movable contactor movable to a position to come in contact with or be separated from the stationary contactor to open or close the circuit. The movable contactor is separately provided for each AC (Alternating Current) phase of R, S, T and N. The movable contactor for each phase includes a plurality of movable conductors (so-called movable arms) so as to divide flowing current for management. Also, each of the plurality of movable conductors is provided with a contact spring which is installed at a rear side thereof to push its corresponding movable conductor toward the stationary contactor so as to keep the stationary contactor coming in contact with the movable conductor in its closed state (i.e., a conducted state, so-called on-state).
Configuration and operation of an exemplary movable contactor according to the related art will be described with reference to FIGS. 1 and 2.
First, the configuration and operation of the movable contactor for the related art air circuit breaker is described with reference to FIG. 1 which is a perspective view of the movable contactor obliquely shown from its upper side in order to illustrate the configuration of the movable contactor for the related art air circuit breaker.
The movable contactor for the related art air circuit breaker shown in FIG. 2 shows a movable contactor of a particular phase among movable contactors provided for each AC phase of R, S, T and N, for example. As shown in FIG. 2, the movable contactor 1 of the particular phase is provided with a plurality of movable conductors 10 for dividing flowing current for management.
Each of the plural movable conductors 10 includes a main contact 2 and an arc contact 3 on its front surface. Upon a closing operation (i.e., upon a switch-on operation), the arc contact 3 of the movable conductor 10 comes in contact with an arc contact of the stationary contactor and thereafter the main contact 2 of the movable conductor 10 comes in contact with a main contact of the stationary contactor, such that the main contact 2 and the arc contact 3 of the movable conductor 10 can contact those of the stationary contactor. The arc contacts are separated from each other after the main contacts come in contact with each other.
Each of the plural movable conductors 10 is provided with a contact spring 8 installed at its rear side to supply an elastic force by which the corresponding movable conductor 10 is pushed toward the stationary contactor such that the stationary contactor can stably come in contact with the movable conductor 10 of the movable contactor 1 upon the closing operation.
An unexplained reference numeral 4 in FIG. 2 designates a pivot shaft portion protruding from a lower side of the movable contactor 1, 5 designates a pivot shaft support for pivotably supporting the pivot shaft portion 4 so as not to be shaken, 6 designates a bus bar for connecting a conducting line to the movable contactor 1, and 7 designates a cage configuring an outer case of the movable contactor 1.
In the meantime, FIG. 1 is a side view of the movable contactor for the related art air circuit breaker, particularly, showing an introduction of arcs into a contact spring. Upon a closing operation, arcs of high temperature and high voltage are introduced between the contact of the movable contactor 1 and the contact of the stationary contactor, for example, along an arc introduction path A of FIG. 1.
Especially, the movable contactor for the related art air circuit breaker has a structure in which upper surfaces of the contact springs 8 are open as shown in FIG. 2. Accordingly, the contact springs are damaged due to an exposure to arcs introduced along the arc introduction path A, which results in a degradation in an elastic force of the contact springs due to impurities adhered thereon. The damage to the contact springs and the degradation in the elastic force thereof cause a decrease in a conducting performance of the air circuit breaker in its on state.
Furthermore, the performance degradation in part of the contact springs causes a current concentration on movable conductors supported by the remaining contact springs. As a result, the contact adhered on the movable conductor cannot cope with large current so as to be melted, which may cause the opening operation not to be performed when a circuit is needed to be broken.
In addition, decrease in the lifespan of the air circuit breaker and increase in a maintenance cost therefore may be caused.